Broadly, the invention relates to a system and method for measuring energy changes in exothermic chemical reactions. More particularly, the invention is directed to a calorimeter apparatus capable of measuring the adiabatic temperature rise, and pressure change, as a function of time, which occurs in a self-heating reaction.
In the commercial production of chemical compounds, the mass of the reactant materials, in relation to the mass of the reactor vessel, is usually a large ratio, such as 10:1. In addition, the total heat capacity of the reactants, as compared to the heat capacity of the reactor, is an even larger ratio. If loss of cooling occurs during the reaction, the reactor usually does not provide an adequate heat sink for absorbing the heat energy liberated by the reaction. In this situation the liberated heat causes the temperature of the reactant mass to rise sharply, and the reaction proceeds at a much faster rate.
When the reaction mass begins to generate more heat than the system can remove, it becomes a self-heating reaction, with corresponding high temperatures and pressures. If cooling cannot be restored, or the frangible relief systems on the reactor cannot relieve the over-pressure condition, the reaction becomes a runaway. In a runaway situation the reactor usually fails.
Because of the situation described above there is a need for a laboratory instrument in which a runaway reaction can be simulated, to evaluate the potential hazard. An instrument capable of providing the critical data required in such a study must have several features not usually found in instruments now available. First of all, the instrument must have a reaction vessel and associated components which closely simulate the structure and operation of a typical chemical plant reactor, such as a Pfaudler reactor. Secondly, the reaction mixture must be continuously stirred to simulate the actual conditions which occur in a plant reactor. A third consideration is that the reaction must be conducted in a truly adiabatic environment to simulate the worst possible condition, i.e. a runaway reaction. To do this, a means must be provided for compensating out the heat capacity contribution of the reactor. The apparatus of this invention answers this need by providing an instrument which incorporates the features set out above.